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C Borst

Publications and source records attributed to C Borst.

At least 91 records · Page 5Linked to original sources
PubMed1996

Fundamental laser-tissue interactions.

Pulsed xenon chloride excimer and holmium laser-tissue interaction is primarily based on tissue water vaporization. Consequently, each ablative laser pulse produces a rapidly expanding and imploding vapour bubble in blood or the target tissue. In experimental studies, explosive water vaporization is the major mechanical cause of observed tissue dissections. By reduction of the induced bubble volume, a reduction in experimentally and clinically observed dissections after coronary excimer laser angioplasty is to be expected. This reduction of mechanical damage, however, in combination with efficient and substantial plaque debulking is the major challenge in the development of laser angioplasty.

Angioplasty, Laser↗
PubMed1995

Paradoxical arterial wall shrinkage may contribute to luminal narrowing of human atherosclerotic femoral arteries.

BACKGROUND: This study was done to assess how local changes in vessel size, together with plaque load, determine luminal narrowing in atherosclerotic arteries. Fifty-one human femoral arteries were analyzed: 32 postmortem and 19 in vivo by 30-MHz intravascular ultrasound. METHODS AND RESULTS: Histological and intravascular ultrasound cross sections were examined every 0.5 cm over an arterial segment 10 to 15 cm long. In each cross section we measured the lumen area and the area circumscribed by the internal elastic lamina (the IEL area). In each arterial segment, the cross section that contained the least amount of plaque was the reference site. For each cross section, the lumen area stenosis was expressed as percent of the lumen area in the reference site. Similarly, the IEL area was expressed as percent of the IEL area in the reference site (the relative IEL area). There was a significant negative correlation between the relative IEL area and the lumen area stenosis percentage (r = -.62, P < .001 for histology and r = -.66, P < .001 for intravascular ultrasound). When lumen area stenosis was less than about 25%, mainly compensatory enlargement was observed. When lumen area stenosis exceeded about 25%, however, mainly a decrease of the IEL area was observed, which is consistent with arterial wall shrinkage. Furthermore, the increase in plaque area does not account for the total loss of luminal area. There was a moderate correlation between an increase in plaque area and reduction of the corresponding lumen area (r = .49 and r = .56 for histology and intravascular ultrasound, respectively). CONCLUSIONS: The decrease in luminal area cannot be attributed to plaque increase alone. Arterial wall shrinkage is a paradoxical mechanism that may contribute to severe luminal narrowing of the atherosclerotic human femoral artery.

Aged↗
PubMed1995

Ultrasound backscatter at 30 MHz from human blood: influence of rouleau size affected by blood modification and shear rate.

High frequency intravascular ultrasound may show a high intensity backscatter from blood which hampers the discrimination between lumen and arterial wall. In this study, the acoustic behaviour of blood at 30 MHz in relation to rouleau size was analyzed. In a Couette viscometer, high frequency (20-40 MHz) backscatter data from normal and modified blood samples from eight volunteers were obtained at shear rates from 0 to 1000 s-1. The acoustic behaviour of blood was quantified by the integrated backscatter power and the spectral slope of the backscatter coefficient. Backscatter from blood depended on rouleau size. At a shear rate of zero, both whole blood and rouleau-enhanced blood showed a 11-dB-higher integrated backscatter power than rouleau-suppressed blood, which itself was 10 dB higher than that of hemolysed blood, the latter showing a 6-dB-higher backscatter than saline. Platelets did not contribute to the backscatter power. Plasma and saline produced no detectable integrated backscatter power other than noise. The spectral slope of whole and rouleau-enhanced blood was small (1 and 0.5, respectively), whereas rouleau-suppressed blood and hemolysed blood (both with a slope of 3.3) behaved almost like a Rayleigh scattering medium (slope = 4). The backscatter from rouleau-suppressed blood showed no shear rate dependence. At low shear rates ( < 0.8 s-1 for integrated backscatter power and < 0.2 s-1 for the spectral slope), whole blood and rouleau-enhanced blood tended to the results from the static situation (no shear). At high shear rates ( > 80 s-1 for integrated backscatter power and >11 s-1 for spectral slope), these samples tended to the results of rouleau-suppressed blood. Ultrasound backscatter at 30 MHz from human blood is only caused by red blood cells. With increasing aggregate (rouleau) size, the integrated backscatter power increased by 11 dB, and the spectral slope decreased from 3.3 to 1.

Blood↗
PubMed1995

Intravascular ultrasound image subtraction: a contrast enhancing technique to facilitate automatic three-dimensional visualization of the arterial lumen.

At 30 MHz, the intravascular ultrasound backscatter of blood confounds the discrimination of the lumen from the arterial wall. This study validates a subtraction method which creates a still-frame image with a sharp demarcation of the lumen. The method involves subtraction of consecutive images and 2D ensemble averaging of the absolute pixel values. Subtraction exploits the dynamic properties of flowing red blood cells. Three phantom arteries were used, with erythrocytes in their lumens and wall. For this reason, it was not possible, in one single original image, to discriminate the blood in the lumen from the phantom wall. Based on 26 consecutive original images, in the mean subtraction image contrast between lumen and phantom wall grey values increased eightfold from 10.9 (5.3-19.2) (mean and range) in the original image to 87.7 (73.6-107.0) (P < 0.001). A sufficiently large contrast increase to allow automatic segmentation was obtained by using five original images (0.3-s acquisition time) for any single mean subtraction image. Low blood flow velocities (down to 0.5 cm/s) did not alter this result. Automatic segmentation of the lumen allowed fast 3D reconstruction of the lumen in all three phantom arteries. In phantom arteries, the intravascular ultrasound image subtraction technique improved contrast between lumen and wall which enabled automated lumen segmentation and fast 3D visualization of both the lumen and defects in the wall.

Arteries↗
PubMed1995

Remodeling of De Novo atherosclerotic lesions in femoral arteries: impact on mechanism of balloon angioplasty.

OBJECTIVES: Using 30-MHz intravascular ultrasound in the human femoral artery, we related the mode of arterial remodeling to the immediate result and the mechanism of balloon angioplasty. BACKGROUND: The atherosclerotic femoral artery may undergo three modes of remodeling in response to plaque formation: compensatory enlargement, failure of compensatory enlargement and paradoxic shrinkage. METHODS: In 83 patients an ultrasound catheter pullback maneuver was performed before and after balloon angioplasty. For each lesion (n = 121), the cross section with the narrowest lumen was selected for further analysis. For each cross section, the lumen area stenosis was expressed as percent of the lumen area at an adjacent reference site. Similarly, the media-bounded area was expressed as percent of the media-bounded area at the reference site. Cross sections were classified into one of three groups based on percent relative media-bounded area: 1) > 105% (group A, compensatory enlargement, n = 24); 2) 95% to 105% (group B, failure of compensatory enlargement, n = 26); and 3) < 95% (group C, arterial wall shrinkage, n = 71). The power of the present study was 99.3% to demonstrate a difference in lumen gain of 2.5 mm2 among groups. RESULTS: The gain in lumen area induced by balloon angioplasty did not differ significantly among the three groups (group A, 7.0 +/- 4.0 mm2 [mean +/- SD]; group B, 8.6 +/- 4.8 mm2; group C, 8.9 +/- 4.9 mm2). Stretch of the media-bounded area was observed in all three groups, but it was significantly larger in group C (7.5 +/- 5.2 mm2) than in the other two groups (group A, 3.9 +/- 5.1 mm2; group B, 5.1 +/- 4.1 mm2). A significantly positive correlation between balloon/media-bounded area ratio and elastic recoil was observed for cross sections in groups A and B (r = 0.71 and r = 0.69, respectively). However, no correlation was observed between balloon/media-bounded area ratio and elastic recoil for cross sections in group C (r = 0.17). CONCLUSIONS: We conclude that lumen gain by balloon angioplasty is not related to the mode of atherosclerotic arterial remodeling. However, the mode of arterial remodeling affects the dilation mechanism.

Aged↗
PubMed1995

Discrimination of intravascular lumen and dissections in single intravascular ultrasound images using subtraction, conventional averaging and saline flush.

With current 30-MHz intravascular ultrasound systems, flowing blood may cause considerable backscatter which in real-time images is characterized by dynamic speckle. However, in a single intravascular ultrasound image (still-frame) the discrimination between arterial lumen and wall may be difficult due to the frozen intraluminal speckle, particularly in the presence of dissections. We compared subtraction, averaging and saline flush as methods to improve the discrimination between arterial lumen and wall in a single image. The real-time images served as gold standard. In 22 patients who underwent peripheral balloon angioplasty, ultrasound images obtained from 84 sites were examined. The sensitivity and specificity of detecting dissections were in the subtraction image 85% and 100%, in the averaged image 57% and 96%, and in the saline flush image 58% and 86%, respectively. Subtraction is a promising method to outline the irregular lumen in a single image.

Aged↗
PubMed1995

Arterial remodeling in atherosclerosis and restenosis: a vague concept of a distinct phenomenon.

Geometric remodeling in atherosclerosis and restenosis comprises a change of the total arterial circumference that, together with plaque growth or neointima formation, determine the lumen of the artery. The change in total arterial circumference relative to a reference cross section ranges from excessive enlargement with an actual increase in lumen to a shrinkage contributing to lumen narrowing. The forces that determine whether an artery shrinks or is able to enlarge as a consequence of atherosclerotic lesions or of post-interventional intimal hyperplasia are unknown but are likely to affect matrix and specifically collagen redistribution. Identifying these forces is of importance because they might be used to promote favorable remodeling. The cellular and humoral triggers of collagen degradation and synthesis, as well as conformation changes of collagen matrices after their deposition, need to be investigated. As with injury-induced intimal hyperplasia and plaque growth in de novo atherosclerosis, injury models may serve as a paradigm for geometric remodeling in atherosclerosis.

Angioplasty↗
PubMed1994

Temperature dependence of the absorption coefficient of water for midinfrared laser radiation.

The dynamics of the water absorption peak around 1.94 microns was examined. This peak is important for the absorption of holmium and thulium laser radiation. To examine the effect of temperature on the absorption coefficient, the transmission of pulsed Ho:YAG, Ho:YAG, Ho:YSGG, and Tm:YAG laser radiation through water of 22 degrees C, 49 degrees C, and 70 degrees C was measured as a function of the thickness of the water layer. From these data the absorption coefficients were determined at the three wavelengths. We found that at all three wavelengths, the absorption coefficients decreased when increasing the temperature. Second, the absorption spectrum of water was measured from 1,850-2,150 nm with a spectrophotometer. It was found that the absorption peak at 1.94 microns (at 22 degrees C) shifts to shorter wavelengths with increasing temperatures, to 1.92 microns at 70 degrees C. A model was developed to predict the temperature distribution incorporating the dynamic change in absorption coefficient. The temperature distributions are compared to the predictions of a model assuming constant optical properties. It is shown in this study that the dynamics of the absorption coefficient has a significant influence on the expected zone of damage and ablation parameters in the 2-microns wavelength range.

Absorption↗
PubMed1994

The cleavage plane in semi-closed endarterectomy of the superficial femoral artery: a histologic study.

PURPOSE: The purpose of this study was to determine the cleavage plane in semiclosed endarterectomy of the superficial femoral artery, a histologic study of endarterectomy cores of 10 consecutive patients was performed. Superficial femoral artery occlusive disease consisted of multiple stenoses in one and an occlusion in the other cases. METHODS: Microscopic paraffin cross-sections were made every half centimeter of the endarterectomy core. The sections were stained with hematoxylin-eosin and with elastica van Gieson. Microscopic studies were conducted of a total of 484 sections. Intima, internal elastic membrane, media, external elastic membrane, and adventitia were identified, if present. RESULTS: When the procedure of separating the diseased intima from the remainder of the arterial wall was commenced, the cleavage plane was located between the internal elastic membrane and the media in most cases. In two cases the cleavage plane was located inside the intima, and in one case parts of the media were removed as well. During passage of the ring stripper through the artery, the location of the cleavage plane changes and extends into the media. In one patient a residual stenosis was located in the segment of the core in which only the intima and internal elastic membrane were removed. In two patients the endarterectomy core contained parts of the external plastic membrane as well. During passage of the ring stripper through the artery, the location of the cleavage plane changes. In some segments the media is left intact, whereas in other segments the media is partially or totally removed. The reason for the variability of the cleavage plane rests in the nature of the pathologic behavior of the atheroma. The tissue necrosis that is part of the atheromatous complex frequently dips beyond the internal elastic membrane into the media and even into the external elastic membrane and adventitia. CONCLUSIONS: The question remains as to whether the location of the cleavage plane has an influence on the long-term results of endarterectomy. Long-term follow-up studies are required to supply us with the answer.

Aged↗
PubMed1994

The relative importance of arterial remodeling compared with intimal hyperplasia in lumen renarrowing after balloon angioplasty. A study in the normal rabbit and the hypercholesterolemic Yucatan micropig.

BACKGROUND: Although arterial renarrowing after angioplasty has been attributed largely to intimal hyperplasia, there has been no systematic effort to correlate the actual hyperplastic tissue mass with angiographic lumen reduction. Using balloon angioplasty in various animal restenosis models, we quantitatively assessed the separate contributions of intimal hyperplasia and arterial remodeling to angiographic late lumen loss. METHODS AND RESULTS: Data used for this study were obtained from experiments of conventional and thermal (37 degrees C or 55 degrees to 90 degrees C) balloon angioplasty-treated femoral and iliac arteries in normal rabbits and conventional balloon angioplasty-treated iliac arteries in Yucatan micropigs fed either a normal or an atherogenic diet. Quantitative angiography was performed immediately before and after intervention and at 3 or 8 weeks thereafter, and late loss in lumen diameter was taken as the difference between arterial diameter immediately after treatment and at 3 or 8 weeks of follow-up. Intimal hyperplasia was quantified histologically as the area of tissue mass within the internal elastic lamina. We observed a consistent discrepancy between the actual late loss seen with angiography and the diameter reduction that could be explained by histological intimal thickness alone in both animal models. This discrepancy ranged from 86 +/- 3% of the late loss in the 8 weeks/37 degrees C group to 77 +/- 22% in the conventional group for rabbits and 52 +/- 23% in an atherogenic diet group (n = 10) to 89 +/- 11% in a normal diet group (n = 6) for pigs. This discrepancy appeared to be due predominantly to reduction of the area circumscribed by the internal elastic membrane, a process that is tentatively designated as arterial remodeling. In both the rabbit femoral artery and in the Yucatan iliac artery, remodeling, not intimal hyperplasia, correlated with angiographic late loss. CONCLUSIONS: In both the normal rabbit and the normal and atherosclerotic pig, restenosis after angioplasty results from both intimal hyperplasia and arterial remodeling. The exact etiology of arterial renarrowing after angioplasty has important implications on the design of antirestenosis drugs and new coronary devices.

Angioplasty, Balloon↗
PubMed1993

Discrimination of the intravascular lumen and dissections in a single 30-MHz US image: use of "confounding" blood backscatter to advantage.

At 30-MHz intravascular ultrasound, the high-intensity backscatter of blood confounds discrimination of the intravascular lumen from the arterial wall. The authors developed and used a subtraction method to visualize the lumen and dissections through cancellation of backscatter from static areas. In two patients who underwent angioplasty of the superficial femoral artery, the residual hyperechoic pattern created by moving blood allowed good differentiation between the wall and lumen or dissections.

Aged↗
PubMed1993

Intraluminal vapor bubble induced by excimer laser pulse causes microsecond arterial dilation and invagination leading to extensive wall damage in the rabbit.

BACKGROUND: Previous in vitro studies demonstrated that during excimer laser ablation of aortic tissue in saline, a fast-expanding and imploding vapor bubble is formed. The present in vivo study was designed to demonstrate the formation of a fast-expanding intraluminal bubble in flowing blood and to assess any damage to the adjacent arterial wall. METHODS AND RESULTS: Excimer laser pulses (one to 10, at 55 mJ/mm2 per pulse) were delivered coaxially in the femoral and iliac arteries of nine normal rabbits. Time-resolved flash photography of dissected arteries in situ demonstrated a 50% diameter increase within 75 microseconds after the laser pulse and a subsequent invagination (150-500 microseconds) that corresponded with the temporal course of the bubble expansion (up to 3.2 mm in diameter) and implosion observed in a hemoglobin solution. One day after laser light delivery, light microscopy (47 arterial segments) showed abrasion of the internal elastic lamina, medial necrosis, and extensive dissection planes filled with red blood cells. The degree (up to 100% medial necrosis) and extent of damage (up to 1.9 mm in length) increased with the number of delivered laser pulses. CONCLUSIONS: In blood, each excimer laser pulse generated a fast-expanding and imploding vapor bubble. In vivo, the intraluminal vapor bubble produced microsecond dilation and invagination of the adjacent arterial segment, which induced dissections and extensive wall damage far beyond the penetration depth of 308-nm laser light (< 100 microns). This unique pattern of extensive wall damage observed in the rabbit might explain the mechanism of dissection observed in humans and might have an impact on the acute and chronic outcome after excimer laser coronary angioplasty.

Angioplasty, Laser↗
PubMed1993

Both increased and decreased platelet adhesion to thermally injured subendothelium is caused by denaturation of von Willebrand factor.

BACKGROUND: Thermal angioplasty methods heat the arterial wall. We related platelet adhesion to the temperature to which subendothelium and purified adhesive proteins had been exposed. METHODS AND RESULTS: Cultured subendothelium, purified von Willebrand factor, collagen types I and III, or fibronectin was applied to glass coverslips. Coverslips were mounted on a heating device that applied a temperature gradient from 30 to 100 degrees C. De-endothelialized umbilical arteries were heated by immersion in phosphate-buffered saline. After cooling to room temperature, the surfaces were perfused with blood at 37 degrees C (shear rate, 1600 sec-1). Compared with 37 degrees C, platelet adhesion to endothelial cell matrix was significantly reduced by 25%, 50% or 75% after heating to 69 +/- 1 degree C (mean +/- SEM, P < .05), 72 +/- 1 degree C, or 75 +/- 1 degree C, respectively. Platelet coverage to umbilical artery subendothelium was in the same way significantly reduced after heating to 71 +/- 1 degree C, or 77 +/- 1 degree C, respectively. In contrast to endothelial cell matrix, however, heating to about 55 degrees C increased platelet coverage from 30 +/- 5% to 54 +/- 6% (P < .05). Both platelet adhesion to von Willebrand factor and monoclonal antibody binding against the GpIb binding site of von Willebrand factor showed a comparable temperature dependence as platelet adhesion to subendothelium, provided the proper von Willebrand factor concentration was used. Platelet adhesion to heated collagen types I and III was increased and maximal at 57 +/- 2 degrees C and 62 +/- 2 degrees C, respectively. Preincubation of collagen III with proteins resulted in decreased platelet adhesion with increasing temperatures. Heating did not affect the reactivity of fibronectin. CONCLUSIONS: In vitro platelet adhesion to human subendothelium is reduced by more than 50% after heating it briefly to more than 74 degrees C. Temperatures in excess of 80 degrees C reduce platelet adhesion by at least 85%. Thermal denaturation of von Willebrand factor is responsible not only for the decreased thrombogenicity above 71 degrees C but also for the increased thrombogenicity near 55 degrees C, provided that the von Willebrand factor concentration is low.

Angioplasty, Balloon↗
PubMed1993

Extensive cryoablation of the left ventricular posterior papillary muscle and subjacent ventricular wall. Impact on mitral valve function and hemodynamics.

Ventricular tachycardias that originate from the inferior left ventricular wall may necessitate transmural ablation involving the posterior papillary muscle of the mitral valve. The effect on mitral valve function and hemodynamics of extensive cryoablation of the left ventricular posterior papillary muscle and subjacent ventricular wall was studied in 16 dogs. Two sham experiments were done. All dogs were studied preoperatively and postoperatively by pulsed Doppler and two-dimensional echocardiography. Left ventricular angiographic and hemodynamic studies were performed preoperatively in six treated dogs and two control dogs and in all dogs at the end of follow-up (1, 3, or 6 months). Postmortem studies were performed in all dogs. The cumulative probability of freedom from mitral regurgitation at 2 months was 0.43 +/- 0.14. Thereafter no new cases of mitral regurgitation could be demonstrated. The angiographic degree of mitral regurgitation was mild in five and moderate in two dogs and did not increase from 3 to 6 months. One dog with acute severe mitral regurgitation died early of heart failure. A significant increase in left ventricular end-diastolic and mean pulmonary capillary wedge pressure of 9.4 +/- 2.5 mm Hg and 6.4 +/- 2.6 mm Hg, respectively, was found in treated dogs at 3 months. These results suggest that extensive cryoablation of the left ventricular posterior papillary muscle and subjacent ventricular wall can be accomplished with an acceptable risk of mild to moderate mitral regurgitation, and without serious detrimental effect on left ventricular function. Retraction is probably the main mechanism of mitral regurgitation.

Angiography↗
PubMed1992

Origin of arterial wall dissections induced by pulsed excimer and mid-infrared laser ablation in the pig.

To study adjacent tissue damage after delivery of holmium, thulium and excimer laser pulses, porcine thoracic aortas were irradiated in vivo. After 3 days, microscopic analysis of 67 craters produced by all three lasers demonstrated large dissections extending from the craters. The mean diameter of the dissections was smaller for excimer-induced craters (1.38 +/- 0.42 mm; n = 22) than for holmium-induced (2.7 +/- 0.87 mm; n = 22) and thulium-induced (2.37 +/- 0.42 mm; n = 14) craters (p less than 0.01 vs. mid-infrared dissections). In addition, microscopic analysis demonstrated necrosis adjacent to the crater. The lateral necrotic zones of the thulium-induced craters were smaller than the holmium- and excimer-induced necrotic zones (p less than 0.01). To identify the origin of the excessive tissue tearing, laser-saline and laser-tissue interaction were compared in vitro by time-resolved flash photography. In saline solution, the mid-infrared lasers showed bubble formation on a microsecond time scale. The excimer laser produced similar bubbles in the vicinity of tissue. For all three lasers, elevation of the tissue surface was shown during in vitro ablation. Dimension (diameter up to 4 mm) and time course (rise time of 100 to 300 microseconds) of bubble formation and tissue elevation were strikingly similar. Thus, tissue dissections are caused by the expansion of a vapor bubble within the target tissue. Coronary dissections after excimer and mid-infrared laser angioplasty might be related to the forceful bubble expansion.

Angioplasty, Laser↗
PubMed1992

Nd:YAG laser-assisted angioplasty in femoropopliteal artery occlusions: "hot" versus "cold" recanalization with transparent contact probe.

Percutaneous recanalization of femoropopliteal artery occlusions (1-21 cm; median, 8 cm) was attempted in 50 patients. A 2.2-mm-diameter contact probe catheter connected to a continuous-wave neodymium yttrium aluminum garnet (Nd:YAG) laser was used. The laser was activated (15 W, 1-second pulses) only if too much resistance was met. Balloon angioplasty was performed after successful traversal of the occlusion. Primary success was achieved in 40 of 50 patients (80%). In 20 cases, recanalization was achieved mechanically (cold group). In the other 20 cases, recanalization was achieved with the help of laser irradiation (hot group: 15-405 J; median, 90 J). Except for the length of the obstruction (longer in the cold group), the two groups did not differ in baseline characteristics. Neither the length of the occlusion nor the duration of symptoms correlated with failure or success or with the delivered laser energy. Cold and hot groups did not differ with regard to functional improvement and angiographic patency at 3 and 12 months (94% +/- 4). Thus, brief laser activation doubled the cold primary success rate, but the major action of the laser contact probe is mechanical remodeling of the obstruction.

Adult↗